U.S. patent application number 11/968385 was filed with the patent office on 2009-07-02 for sensor apparatus for measuring and detecting acetylene and hydrogen dissolved in a fluid.
This patent application is currently assigned to General Electric Company. Invention is credited to Elena Babes-Dornea, Yves Grincourt.
Application Number | 20090166197 11/968385 |
Document ID | / |
Family ID | 40796783 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090166197 |
Kind Code |
A1 |
Grincourt; Yves ; et
al. |
July 2, 2009 |
SENSOR APPARATUS FOR MEASURING AND DETECTING ACETYLENE AND HYDROGEN
DISSOLVED IN A FLUID
Abstract
A fuel cell sensor is provided for detecting the presence of
acetylene and hydrogen in a fluid. The sensor includes a sensing
element having first and second gas diffusing electrodes spaced
from one another. The first gas diffusing electrode can be used for
sensing acetylene. The second gas diffusing electrode can be used
for sensing hydrogen. A fuel cell spacer having an acidic
electrolyte is disposed between the sensing element and a common
electrode. The sensing element can be configured to have a specific
ratio of the area between the first gas diffusing electrode in
relation to the area of the second gas diffusing electrode.
Inventors: |
Grincourt; Yves; (Ottawa,
CA) ; Babes-Dornea; Elena; (Pierrefonds, CA) |
Correspondence
Address: |
GE ENERGY GENERAL ELECTRIC;C/O ERNEST G. CUSICK
ONE RIVER ROAD, BLD. 43, ROOM 225
SCHENECTADY
NY
12345
US
|
Assignee: |
General Electric Company
|
Family ID: |
40796783 |
Appl. No.: |
11/968385 |
Filed: |
January 2, 2008 |
Current U.S.
Class: |
204/412 |
Current CPC
Class: |
G01N 27/4045
20130101 |
Class at
Publication: |
204/412 |
International
Class: |
G01N 27/26 20060101
G01N027/26 |
Claims
1. A fuel cell sensor for detecting the presence of at least one of
acetylene and hydrogen in a fluid, comprising: a sensing element
comprising first and second gas diffusing electrodes spaced from
one another, said first gas diffusing electrode for sensing
acetylene and said second gas diffusing electrode for sensing
hydrogen: a common electrode: a fuel cell spacer having an acidic
electrolyte disposed between said sensing element and said common
electrode; wherein, said sensing element being configured to have a
specific ratio of the area of said first gas diffusing electrode in
relation to the area of said second gas diffusing electrode.
2. The fuel cell sensor of claim 1, wherein said specific ratio is
between about 1:1 to about 5:1.
3. The fuel cell sensor of claim 1, wherein said specific ratio is
between about 1:10 to about 10:1.
4. The fuel cell sensor of claim 1, wherein: said first gas
diffusing electrode comprises a gas porous gold film and an ion
exchange membrane; and said second gas diffusing electrode and said
common electrode comprise a graphite layer and a platinum-carbon
layer.
5. The fuel cell sensor of claim 1 wherein said first and second
gas diffusing electrodes are spaced from one another by an
insulating adhesive.
6. The fuel cell sensor of claim 1 further comprising: a gas
permeable membrane located between said fluid and said sensing
element, said gas permeable membrane comprises a fluoropolymer film
and a porous support.
7. The fuel cell sensor of claim 1, wherein said acidic electrolyte
comprises, at least one of, sulfuric acid (H.sub.2SO.sub.4), fumed
silica (SiO.sub.2), and water (H.sub.2O).
8. The fuel cell sensor of claim 1, wherein said fuel cell spacer
comprises polypropylene.
9. A fuel cell sensor for detecting the presence of, at least one
of, acetylene and hydrogen in a fluid, comprising: at least one
first sensing element for sensing acetylene; at least one second
sensing element for sensing hydrogen; a common electrode; a fuel
cell spacer having an acidic electrolyte disposed between both said
first and second sensing elements and said common electrode.
10. The fuel cell sensor of claim 9, wherein: said first sensing
element comprises a gas porous gold film and an ion exchange
membrane; and said second sensing element and said common electrode
comprise a graphite layer and a platinum-carbon layer.
11. The fuel cell sensor of claim 9, comprising: two first sensing
elements; and two second sensing elements.
12. The fuel cell sensor of claim 9, comprising: three first
sensing elements; and one second sensing element.
13. The fuel cell sensor of claim 9, further comprising: a gas
permeable membrane located between said fluid and said at least one
first sensing element and said at least one second sensing element,
and said gas permeable membrane comprises a fluoropolymer film and
a porous metallic support disk.
14. The fuel cell sensor of claim 9, wherein said acidic
electrolyte comprises a mixture of sulfuric acid (H.sub.2SO.sub.4),
fumed silica (SiO.sub.2) and water (H.sub.2O).
15. The fuel cell sensor of claim 9, wherein said fuel cell spacer
comprises polypropylene.
16. An electrochemical sensing element comprising: a plurality of
sensing electrodes; and a common electrode; wherein said
electrochemical sensing element can be used for the simultaneous
measurement or quantification of a plurality of different gases
dissolved in a fluid.
17. The electrochemical sensing element of claim 16, wherein said
plurality of sensing electrodes further comprise: at least one
first electrode sensitive to acetylene; and at least one second
electrode sensitive to hydrogen; and at least one common electrode;
wherein said electrochemical sensing element can be used for the
simultaneous measurement of acetylene and hydrogen dissolved in
said fluid.
18. The electrochemical sensing element of claim 17, wherein said
at least one first electrode and said at least one second electrode
can detect acetylene gas or hydrogen gas in different
proportions.
19. The electrochemical sensing element of claim 17, wherein: a
first signal measured between said at least one first electrode and
said at least one common electrode is proportional with the
concentration of acetylene in said fluid; and a second signal
measured between said at least one second electrode and said at
least one common electrode is proportional with the concentration
of hydrogen in said fluid.
20. The electrochemical sensing element of claim 17, wherein a
surface ratio between said at least one first electrode and said at
least one second electrode is about 2:1 to about 4:1.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to a sensor
apparatus for monitoring the presence of acetylene and hydrogen in
a fluid such as, for example, an insulating fluid. More
specifically, the invention relates to a sensor apparatus in which
the concentration of acetylene and hydrogen dissolved in a fluid
are determined by the measure of an electric current generated by
electrochemical oxidation of the acetylene and hydrogen at
detection electrodes.
[0002] The following will deal, by way of example only, with the
detection of constituents in a fluid that may be an insulating or
dielectric fluid. Electrical systems are well known in the art
which use an insulating fluid as an insulating substance; these
systems include for example transformers, circuit breakers and the
like.
[0003] It is known that, in the event of a disturbance or
malfunction of an above mentioned type of device or system, the
result may be the production of one or more gases in the insulating
fluid; this may occur for example if a device is working at high
temperature or high conditions of electrical stress therein. Such
conditions may also produce undesired moisture and/or one or more
breakdown products of the dielectric material of the insulating
system (i.e. insulating fluid). If such abnormal conditions are
allowed to continue uncorrected, this may lead to irreparable
damage to the electrical system. A timely (e.g. more or less
immediate) detection and/or diagnosis of any such abnormal
operation of an electrical apparatus is thus advantageous in order
to be able to avoid irreparable harm to such a system.
[0004] Accordingly, various monitoring devices and systems have
been proposed for the detection of any incipient failure conditions
such as for example any undesired increase of the concentration of
a fault gas (e.g. a combustible gas such as for example, hydrogen
gas (H.sub.2), carbon monoxide gas (CO), methane gas (CH.sub.4),
ethane gas (C.sub.2H.sub.6), ethylene gas (C.sub.2H.sub.4),
acetylene gas (C.sub.2H.sub.2) and the like or a non-combustible
gas such as for example, carbon dioxide (CO.sub.2), moisture (e.g.
water or H.sub.2O), a breakdown product, contaminant substance,
and/or the like contained (e.g. dissolved) in the insulating
fluid.
[0005] Some such detection and/or monitoring systems are, for
example, described in U.S. Pat. No. 4,112,737 (Morgan), U.S. Pat.
No. 4,293,399 (Belanger et al), U.S. Pat. No. 4,271,474 (Belanger
et al), U.S. Pat. No. 5,070,738 (Morgan), U.S. Pat. No. 5,271,263
(Gibeault) and U.S. Pat. No. 5,738,773 (Criddle et al.).
[0006] U.S. Pat. No. 5,738,773 for example illustrates a fuel cell
arrangement for detecting oxidizable components of a gas or vapor.
The fuel cell comprises first electrode means and second counter
electrode means which are connected by an acidic electrolyte. The
electrochemical oxidation of a fuel component in the gas results in
the formation of a potential difference between the first and
second electrode means; the resultant current and/or potential
difference can be detected and associated with the presence and/or
concentration of combustible gas detected thereby.
[0007] U.S. Pat. No. 4,293,399, for example, describes how the
concentration of gaseous hydrogen dissolved in a fluid may be
determined by a measure of an electric current generated by
electrochemical oxidation of the gaseous hydrogen at an electrode
of the detector; i.e. by a measure of a current generated in
response to the presence of hydrogen (in a gas). The prior art
detecting and measuring means described in this U.S. patent
comprises a polymeric membrane permeable to hydrogen gas for
contact with a fluid containing dissolved hydrogen gas; an
electrolyte capable of facilitating oxidation of the hydrogen gas
diffused through the polymeric membrane at a first electrode and
reduction of an oxygen-containing gas such as air at a second
electrode; and a measuring device connected to the fuel cell for
measuring the intensity of the electrical current generated by the
electrochemical reaction of oxidation of the hydrogen gas, this
intensity being proportional to the concentration of hydrogen in
the fluid.
[0008] It is advantageous for such monitoring (e.g. detection)
devices, as described above, to be able to provide an accurate as
possible detection and/or diagnosis of the incorrect operation of
systems such as, for example, transformers, circuit breakers, shunt
reactors or any electro-apparatuses using a dielectric fluid as an
insulating substance such as a dielectric liquid (e.g. a dielectric
oil) or a dielectric gas (e.g. SF.sub.6 gas).
[0009] A number of the above mentioned prior art monitoring devices
or systems may be limited in that the sample gas received by the
detector may be a mixture containing multiple gases, having a
relatively low concentration of a target gas which it is desired to
detect or monitor; e.g. a low concentration of acetylene gas
relative to hydrogen gas. In such case, the low concentration of a
target gas relative to the other gases present in a sample gas may
be such that one or more of the other gases may interfere with the
measurement of a predetermined target gas(es). In other words, the
precision of the results of the detecting or monitoring device may
thus be less than is desired; i.e. due to that fact that one or
more extraneous gases may interfere with the reading of the target
gas (e.g. acetylene). Another limitation of the prior art devices
is that only one gas can be detected.
[0010] The presence, concentration and evolution of even very low
concentrations of acetylene and hydrogen dissolved in a dielectric
fluid, such as for example a dielectric oil, is a particularly
useful indicator of the processes occurring (e.g. default gas
production) in the insulated electrical equipment. As mentioned, in
addition to acetylene and hydrogen, the dielectric fluid may
contain other dissolved gases, such as carbon monoxide, ethylene,
ethane, methane, etc. A reliable analysis of acetylene and hydrogen
thus requires a detector having an enhanced selectivity for
acetylene at very low concentrations in the presence of other such
dissolved gases (e.g. hydrogen).
[0011] Accordingly, it would be advantageous to have a detector for
the specific detection, measuring and monitoring of acetylene and
hydrogen dissolved in a dielectric fluid (e.g., a dielectric oil
used in a transformer).
BRIEF SUMMARY OF THE INVENTION
[0012] The present invention, in accordance with one aspect,
provides a fuel cell sensor for detecting the presence of acetylene
and hydrogen in a fluid. The sensor includes a sensing element
having first and second gas diffusing electrodes spaced from one
another. The first gas diffusing electrode can be used for sensing
acetylene. The second gas diffusing electrode can be used for
sensing hydrogen. A fuel cell spacer having an acidic electrolyte
is disposed between the sensing element and a common electrode. The
sensing element can be configured to have a specific ratio of the
area between the first gas diffusing electrode in relation to the
area of the second gas diffusing electrode.
[0013] In accordance with another aspect, the present invention
provides a fuel cell sensor for detecting the presence of acetylene
and hydrogen in a fluid. The sensor includes at least one first
sensing element for sensing acetylene, and at least one second
sensing element for sensing hydrogen. A fuel cell spacer having an
acidic electrolyte is disposed between both the first and second
sensing elements and the common electrode.
[0014] The present invention, in accordance with yet another
aspect, provides an electrochemical sensing element having a
plurality of sensing electrodes and a common electrode. The
electrochemical sensing element can be used for the simultaneous
measurement or quantification of a plurality of different gases
dissolved in a fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is an exploded, cross-sectional illustration of an
example fuel cell sensor assembly;
[0016] FIG. 2 is an enlarged, cross-sectional illustration of a
fuel cell and fuel cell cover assembly;
[0017] FIG. 3 is an exploded, cross-sectional illustration of
another embodiment of a fuel cell sensor;
[0018] FIG. 4 is an exploded, cross-sectional illustration of
another embodiment of the fuel cell sensor;
[0019] FIG. 5 is a top plan illustration of one embodiment of the
first sensing means;
[0020] FIG. 6 is a top plan illustration of another embodiment of
the first sensing means;
[0021] FIG. 7 is a cross-sectional illustration of the sensor
according to one embodiment of the present invention;
[0022] FIG. 8 is a top plan illustration of another embodiment of
the first sensing means.
[0023] FIG. 9 is a cross-sectional illustration of the sensor shown
in FIG. 8.
[0024] FIG. 10 is a top plan illustration of another embodiment of
the first sensing means.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Various types of electrical equipment can experience
electrically and/or thermally induced damage. Electrical equipment
can include, but are not limited to, power transformers, reactors,
auto transformers, instrument transformers, arc furnace
transformers, rectifier transformers, distribution transformers,
tap changers and oil-filled power cables. Power transformers, for
example, operate continuously and are subject to extremes of
temperature. The insulation used in transformers must be extremely
durable and resistant to degradation. Typically, insulating oil
and/or cellulosic insulation are used as the insulating mediums.
The insulating oil and cellulosic insulation can break down and
decompose into its constituent elements when subjected to
electrical discharges or elevated temperatures.
[0026] The insulating oil used in transformers can begin to
decompose when the temperature reaches 150 degrees C. Generally,
hydrogen is generated by thermal decomposition. At the higher
temperature levels acetylene can also be generated. Partial
electrical discharges (i.e., corona) and low level arcing generate
hydrogen and small amounts of acetylene. High level arcing
generates acetylene and hydrogen.
[0027] The presence of acetylene and hydrogen, and other gases, can
be indicative of the overall health and condition of the
transformer. Early detection of rising levels of specific gases or
constituents can be used to correct for failing insulation or
component malfunction. When levels of hydrogen are more than about
100 ppm and/or acetylene are more than about 35 ppm in the
insulating oil, the equipment in question should be monitored
closely. If the levels of hydrogen and/or acetylene approach or
exceed these levels, a faulty component or other failure could be
indicated. Accordingly, it would be very desirable to detect these
conditions early and service any equipment before a catastrophic
failure occurs.
[0028] In accordance with aspects of the present invention, a fuel
cell sensor is provided that can simultaneously detect multiple
gases in a fluid (e.g., a dielectric fluid). In some embodiments of
the invention, acetylene and hydrogen are detected. However, the
invention also contemplates detecting other gases and two or more
different gases simultaneously. In one embodiment, the fuel cell
sensor comprises one or more electrodes for detecting acetylene and
one or more electrodes for detecting hydrogen. In other aspects one
electrode can be segmented into two or more sections, where one
section can be configured to detect acetylene and the other section
can be configured to detect hydrogen. In additional aspects, the
ratio between the area of the two sections (i.e., the acetylene
detecting section and the hydrogen detecting section) can be
adjusted for specific applications. For example, the ratio of the
area of the two sections could range from about 1:1 (i.e., each
section of equal area) to about 5:1 (i.e., the acetylene detecting
area is five times greater than the hydrogen detecting area). The
sensor can be configured to have a greater area for the acetylene
detecting electrode or a greater area for the hydrogen detecting
electrode.
[0029] The various embodiments of the present invention, described
herein, provide a sensor instrument that can be used as an early
warning device that can alert operations and maintenance personnel
to developing fault conditions that could lead to equipment
failures and unscheduled outages. The outputs of the sensor can be
used to warn personnel when diagnostic or remedial actions are
needed.
[0030] FIG. 1 illustrates a detailed, exploded view of one
embodiment of a fuel cell sensor 100 for measuring acetylene and
hydrogen in fluids, according to the present invention. The sensor
100 includes a cavity 1 for facilitating diffusion of acetylene and
hydrogen from an external fluid. A thermistor 2 can be housed
within the base portion to sense the temperature of the probe body.
A plurality of O-rings 3, 5, 11, 13, 17, 18, 20. 29 and 34 seal off
the internal components of the sensor. A membrane 4 can be placed
between O-rings 3 and 5 to prevent the fluid from entering into the
central portion of the sensor 100. The membrane 4 permits the
diffusion of selected gases (e.g., acetylene and hydrogen) but
prevents the fluid (e.g., dielectric oil used in a transformer)
from passing therethrough. Teflon.RTM. is one example of any
suitable membrane that could be used for membrane 4. In one
specific embodiment, the membrane 4 could be a Teflon.RTM. membrane
1 mil in thickness (1 mil= 1/1000 of an inch). Any membrane capable
of passing selected gases (e.g., acetylene and hydrogen) and
preventing the passage of the target fluid (e.g., dielectric oil)
would suffice. A porous support disk 6 can be placed next to the
membrane 4 to provide rigidity to the membrane 4. The porous
support disk could be any rigid material that will allow the
selected gases to pass therethrough (e.g., stainless steel or any
porous support of appropriate material).
[0031] A fuel cell cup 7 receives the fuel cell detection assembly,
and is secured to the base portion via washer 8 and bolt 9. A
membrane 10 can be placed at the bottom of the cup 7. The membrane
can be comprised of a GORE-TEX.RTM. (a registered trademark of W.L.
Gore & Associates) material or other suitable membrane. An
O-ring 11 can be used to seal the bottom of the fuel cell body 12
to the fuel cell cup 7. A pair of electrodes 14-1 and 14-2 are
placed on opposite ends of a fuel cell spacer 15. The fuel cell
spacer 15 includes a central cavity filled with an acid gel
electrolyte. The central cavity passes from electrode 14-1 to
electrode 14-2. A fuel cell cover 19 can be attached to fuel cell
body 12 with any suitable fastener.
[0032] Additional membranes 22 and 23 can be placed above the fuel
cell cover 19. In one embodiment the membrane 22 could be a
Teflon.RTM. (a registered trademark of DuPont) material of about 2
mils in thickness, and the membrane 23 could be a GORE-TEX.RTM.
material of about 7 mils in thickness. A fuel cell cover plate 24
can be secured to the fuel cell cup 7 by the use of appropriate
fasteners (e.g., washer 25 and bolt 26). A salt bag 27 can be used
to maintain a substantially constant moisture level (e.g., about
20%) inside the senor. The salt bag 27 can be partially or
completely enveloped by a membrane 28. In one embodiment, membrane
28 could be comprised of a GORE-TEX.RTM. material.
[0033] The probe cap 30 can be secured to the base portion with
bolt 32 or any other suitable fastening means. A load resistor 31
is connected to connector 33, and is used to obtain the voltages
between electrodes 14-1 and 14-2. A ventilation membrane 35 and
vent cover 36 are secured to the probe cap with the use of washer
37 and screw 38. The ventilation membrane allows ambient air
(including oxygen) to enter the probe body and reach common
electrode 14-2. Bleed screw 39 can be used to take physical samples
of the fluid being monitored.
[0034] FIG. 2 shows an enlarged view of one embodiment of the fuel
cell sensor. Spacer 15 includes an acidic electrolyte 210 contained
in a central cavity. The common electrode 14-2 is placed at one end
of the cavity and the sensing electrode 14-1 is placed at the
opposite end of the cavity in spacer 15. Electrical contact is made
to electrodes 14-1 and 14-2 via a plurality of lead wires. Lead
wire 201 can be connected to sensing electrode 14-1 and lead wire
202 can be connected to common electrode 14-1. In some embodiments
lead wire 14-1 may comprise a plurality of leads, where each lead
is connected to a different portion of electrode 14-1. Output of
the sensor 100 is measured between the sensor leads 14-1 and 14-2
through a resistor 31 and connector 33 as illustrated in FIG.
1.
[0035] FIG. 3 illustrates another embodiment of the present
invention, with like elements indicated by the same numerals as in
FIGS. 1-2. In this embodiment, sensing electrode is comprised of a
plurality of distinct sensing electrodes 305 and 310. For example,
electrode 305 could be an acetylene detecting electrode and
electrode 310 could be a hydrogen detecting electrode. Even though
only one electrode of each type is indicated, there could be
multiple electrodes 305 for sensing acetylene, and/or multiple
electrodes 310 for sensing hydrogen. A wire lead 302 can be used
for connecting to the common electrode 14-1. Wire lead 320 can be
used to connect to acetylene detecting electrode 310, and wire lead
325 can be used to connect to hydrogen detecting electrode 305. The
wire leads in contact with the electrodes can be made of noble
metals (e.g., platinum or gold). The noble metal leads can then be
soldered to another wire lead which can be formed of any suitable
metal, including but not limited to, copper, aluminum, etc.
[0036] In this embodiment, two load resistors (which may have
different resistances) can be connected to the sensing electrodes.
Resistor 330 can be connected to the acetylene detecting electrode
310 via lead 302. Resistor 345 can be connected to the hydrogen
detecting electrode 305 via lead 325. In one embodiment, resistor
330) can be a fixed load resistance of 2200 ohms, and resistor 345
can be a fixed load resistance of 500 ohms.
[0037] FIG. 4 illustrates an exploded, perspective view of elements
7 to 24 of FIG. 3. Sensing electrodes 305, 310 are shown to
comprise four sensing electrodes in this view. For example, in this
embodiment, one could employ one to three acetylene sensing
electrodes 310, and one to three hydrogen detecting electrodes 310.
The variation on the number and surface area of the multiple
sensing electrodes are described in more detail hereafter.
[0038] In one embodiment, and referring to FIG. 5, the sensing
electrode 14-1 can comprise a multi-sectioned electrode, with each
section responsive to a different constituent (e.g., acetylene or
hydrogen). An acetylene responsive section 502 and a hydrogen
responsive section 504 are both arranged on electrode 14-1. An
adhesive 506 electrically insulates and bonds the two sections. The
adhesive 506 is preferably a silicon, acid resistant adhesive, and
one such adhesive is the Dow Corning.RTM. (a registered trademark
of Dow Corning Corporation) 3145 adhesive/sealant. The electrodes
502 and 504 are shown located generally next to each other, but the
layout of the electrodes 502 and 504 could take any form. For
example, electrode 502 could be placed around electrode 504, where
electrode 504 generally comprises a circular shape and electrode
502 generally comprises a "doughnut" like shape. The interface
between the two electrodes 502 and 504 could be a jagged edge, an
arcuate edge or a stepped edge, in addition to a linear edge as
shown in FIG. 5.
[0039] The acetylene detecting electrode portion 502 can be
comprised of gold, i.e. a gold electrode means. In accordance with
the present invention the acetylene detecting electrode portion 502
(e.g. a gold electrode) may have an electro-catalytic activity for
favoring the oxidation of acetylene as against the oxidation of
gases like hydrogen, carbon monoxide, ethylene, methane, ethane and
the like. The specificity of a gold electrode means for the
electrochemical oxidation of acetylene may be enhanced by using
modified electrode structures. In accordance with the present
invention the acetylene detecting electrode portion 502 may for
example comprise or consist of a gas porous gold film or layer
interfacing a solid ion conducting substrate or ion exchange
membrane, i.e. such that the electrode has a gold/substrate
interface zone wherein gold is dispersed within the matrix of the
substrate (e.g. at least adjacent the surface boundary of the
substrate. The solid ion conducting/exchange membrane may be for
example a perfluorosulfonic acid film, a perfluorosulfonic
acid/PTFE copolymer film, the above mentioned Nafion.RTM.
membrane(s) available from DuPont, or any other suitable ion
exchange film.
[0040] The hydrogen detecting electrode 504 may be any other
electrode means having electro-catalytic activity for the reduction
of hydrogen. The hydrogen detecting electrode 504 may be a noble
metal electrode; for example, a platinum electrode or a
platinum-carbon electrode, or at least one noble metal/carbon
combination and a polymeric hydrophobic binder. The hydrogen
detecting electrode 504 may also comprise a platinum-carbon layer
adhered to a graphite layer (e.g., a graphite paper). The common
electrode 14-2 can be configured of the same materials as the
hydrogen detecting electrode 504.
[0041] The electrode 14-1 as shown in FIG. 5 has a ratio between
the area of the acetylene electrode 502 and the hydrogen electrode
504 of about 1:1. However, this ratio can be changed or adjusted to
increase the electrode's sensitivity to specific gases or
constituents.
[0042] FIG. 6 shows an electrode 14-1 having a ratio of about 3:1
for the area between the acetylene electrode 602 and the hydrogen
electrode 604. The adhesive portion is indicated by 606. The ratio
of the area of the acetylene electrode to the area of the hydrogen
electrode can range between about 10:1 to about 1:10, or other
ratios as the specific application may require. When the two gases
to be detected are acetylene and hydrogen, a preferred range is
about 1:1 to about 5:1 for the acetylene/hydrogen electrode surface
area ratio.
[0043] FIG. 7 shows a cross-sectional view of a portion of one
embodiment of the fuel cell sensor. The fuel cell spacer 15 has a
central via filled with an acid gel electrolyte 710. The common
electrode 14-2 is comprised of a graphite paper layer 720 and a
Pt--C (platinum-carbon) layer 722. Similarly, the hydrogen
detecting electrode 704 portion is also comprised of a graphite
paper layer 720 and a Pt--C (platinum-carbon) layer 722. The
hydrogen detecting electrode 704 also can include a Teflon.RTM.
overlayer 724. The acetylene detecting electrode 702 is comprised
of a Nafion.RTM. membrane layer 732 and a gold layer 734. An
electrically insulating adhesive 740 bonds the acetylene detecting
electrode and the hydrogen detecting electrode together, and one
such adhesive is the Dow Coming.RTM. 3145 adhesive/sealant.
[0044] The acidic electrolyte 710 used is to be of such a
composition so as to enable the occurrence of the reaction of
electrochemical oxidation of the acetylene at the acetylene
electrode 702 and hydrogen at the hydrogen electrode 704 and that
of reduction of oxygen at the common electrode 14-2 (located at the
bottom of FIG. 7); in general the electrolyte is acidic. For that
purpose, any type of acidic electrolyte respecting the
electrochemical operation principle of the detector in accordance
with the present invention may be used. Thus the oxido-reduction
reaction can be initiated by means of an electrolyte constituted by
an acid, such as phosphoric acid, sulfuric acid or perchloric acid.
The electrolyte may be a gel electrolyte, i.e. an electrolyte
gelled by a conventional gelling agent(s) such as Cab-O-Sil.RTM.
(registered trademark of the Cabot Corp.) fumed silica. It may, for
example, be a gel electrolyte comprising sulfuric acid. On the
other hand, the electrolyte may be a solid acidic proton conductor
electrolyte, which may for example be a solid polymeric
electrolyte; the electrolyte may in particular be a solid ion
conducting substrate such as for example a perfluorosulfonic acid
polymers. One type of such solid electrolytes are the Nafion.RTM.
Perfluorosulfonic acid polymers. Hereinafter, these types of
membranes or substrates will unless otherwise indicated be referred
to simply as Nafion.RTM.. Other proton conducting membranes or
substrates may for example be obtained from Dow Coming.RTM.. The
acidic electrolyte may also be comprised of sulfuric acid
(H.sub.2SO.sub.4), fumed silica (SiO.sub.2) and water
(H.sub.20).
[0045] FIG. 8 shows a top, plan view of another embodiment of the
present invention. The acetylene and hydrogen detecting electrodes
can be comprised of multiple electrodes housed within a single
device. In this embodiment, and as one example only, the sensor 100
can include two acetylene detecting electrodes 802 and two hydrogen
detecting electrodes 804. The electrodes 802, 804 can be disposed
over four individual cavities filled with an acid gel electrolyte.
One common electrode can be arranged on the opposite side of the
electrolyte filled cavities. The use of four electrodes are for
example only, and any number of acetylene and/or hydrogen detecting
electrodes could be arranged within sensor 100.
[0046] FIG. 9 illustrates an angled, side view of the sensor of
FIG. 8. One acetylene electrode 802 and two hydrogen electrodes 804
can be seen on top of spacer 15. In this view, three cavities can
be seen and are shown in phantom, and these cavities are filled
with an acid gel electrolyte 910. The common electrode 14-2 is
comprised of a graphite paper layer 920 and a platinum-carbon layer
922. The common electrode 14-2 spans all four cavities under
electrodes 802 and 804. The hydrogen detecting electrodes 804 are
comprised of a graphite paper layer 920 and a platinum-carbon layer
922. The acetylene detecting electrodes 802 are comprised of a
Nafion.RTM. membrane 932 and a gold layer 934.
[0047] FIG. 10 illustrates a top plan view of another embodiment of
the present invention. In this embodiment, three acetylene
detecting electrodes 802 are arranged on spacer 15 with one
hydrogen detecting electrode 804. The three acetylene detecting
electrodes will increase the sensitivity of the device to acetylene
while reducing or maintaining the sensitivity to hydrogen. This
embodiment has a surface area ratio of acetylene to hydrogen
detecting electrodes of 3:1.
[0048] The acetylene and hydrogen detecting electrodes can be
connected to the common electrode through a suitable fixed load
resistance (e.g., 500 to 2200 ohms). In one embodiment, a fixed
load resistance of 2200 ohms can be connected to the acetylene
detecting electrode(s), and a fixed load resistance of 500 ohms can
be connected to the hydrogen detecting electrode(s). Any suitable
electronic signal measuring means can be attached across the load
resistances so as to be able to permit the measuring of the
voltages generated by the oxido-reduction reactions occurring
between (1) the acetylene detection electrodes and the common
electrode, and (2) the hydrogen detection electrode(s) and the
common electrode. The electronic signal measuring means can be
connected to any suitable display means to provide a visual reading
with respect to the concentrations of acetylene and hydrogen. The
signals generated by the fuel cell is essentially a current having
an intensity proportional to the acetylene content and the hydrogen
content in the fluid of interest.
[0049] The sensor device 100 can be used for the simultaneous
detection of both acetylene and hydrogen gas in a fluid (e.g., a
transformer's dielectric oil). The sensor can also detect the
respective proportions (even if they are different) of each gas.
The separate signal measured between the acetylene sensing
electrode and the common electrode is proportional with the
concentration of acetylene in the fluid to be analyzed. The
separate signal measured between the hydrogen sensing electrode and
the common electrode is proportional with the concentration of
hydrogen in the fluid to be analyzed. As described previously, the
sensitivity of the sensor can be made more sensitive to acetylene
by increasing the surface area of the acetylene detecting
electrode(s) in relation to the surface area of the hydrogen
detecting electrode(s). Conversely, the sensitivity of the sensor
can be made more sensitive to hydrogen by increasing the surface
area of the hydrogen detecting electrode(s) in relation to the
surface area of the acetylene detecting electrode(s).
[0050] The sensor device 100 was described primarily with reference
to detecting acetylene and hydrogen. However, the sensor device
could be used to detect other gases or fluid constituents as well.
In addition, one, two, three or more gases could be detected by the
use of suitable electrodes housed within a single sensor device.
Other constituents or gases, including but not limited to, hydrogen
(H.sub.2), carbon monoxide (CO), methane (CH.sub.4), ethane
(C.sub.2H.sub.6), ethylene (C.sub.2H.sub.4), and acetylene
(C.sub.2H.sub.2) can be detected and measured with the sensor
herein described.
[0051] While the invention has been described in terms of various
specific embodiments, those skilled in the art will recognize that
the invention can be practiced with modification within the spirit
and scope of the claims.
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